1. Field of the Invention
The present invention relates to a solenoid valve, a flow-metering valve, a high-pressure fuel pump and a fuel injection pump.
2. Description of Related Art
A solenoid valve used in a fuel injection pump to serve as a flow-metering valve for metering a flow of liquid that is supplied through a liquid inlet port and outflows through a liquid outlet port is disclosed in, for example, Japanese Examined Patent Publication No. S50-6043 (corresponding to U.S. Pat. No. 3,709,639), Japanese Unexamined Patent Publication No. H10-141177 (corresponding to U.S. Pat. No. 6,116,870) and Japanese Unexamined Patent Publication No. 2002-48033. Each fuel injection pump disclosed in the above publications includes the flow-metering valve disposed at a fuel inlet port side of a fuel pump chamber. The flow-metering valve is opened and closed to intermittently enable communication between the fuel pump chamber and the fuel inlet port. Then, an electromagnetic driving member is energized to control closing timing for closing a valve of the flow-metering valve when fuel is compressed, thereby adjusting a fuel pump quantity.
In the flow-metering valve disclosed in the above-described publications, a mobile member is displaced by a magnetic attractive force generated when the electromagnetic driving member is energized, so that the flow-metering valve is closed or is kept open. In the above-described structure, where the mobile member spaced away from a magnetic force generation source is displaced by the magnetic attractive force, a large magnetic attractive force is necessary to attract the mobile member. As a result, there may be disadvantages that the electromagnetic driving member needs to be large and that an energy consumption is increased to generate the magnetic attractive force. Also, in the above-described structure where the mobile member is attracted from a position spaced away from the mobile member, the magnetic attractive force needs to be enhanced so that a response speed to the energization of the electromagnetic driving member is enhanced to quickly displace the mobile member by the magnetic attractive force. The magnetic attractive force also needs to be enhanced so that a clearance may be increased in order to increase an area of a passage when the flow-metering valve is open. As a result, there may be disadvantages that the electromagnetic driving member needs to be large and that energy consumption is increased to generate the magnetic attractive force.
Also, a normally-closed-type solenoid valve, which is opened by a differential pressure between an inlet port side and an outlet port side, is disclosed, for example, in Japanese Unexamined Patent Publication No. 2002-521616 corresponding to U.S. Pat. No. 6,345,608. According to a control valve (a solenoid valve) shown in FIGS. 3 and 4 in Japanese Unexamined Patent Publication No. 2002-521616, a valve member is biased by a spring 68 (a first bias member) in a valve closing direction for closing the control valve. Also, a mobile member (a mobile core) is biased by a spring 64 to be spaced away from the valve member. When an intake stroke in a pump chamber is performed, a pressure in the pump chamber is decreased to become lower than a pressure in a fuel connection part. Thus, the valve member is detached from a valve seat by the differential pressure therebetween against a bias force of the spring 68.
A control unit (driving circuit) starts energizing an electromagnet immediately before the intake stroke is finished. Then, the mobile core is attracted to the electromagnet against a bias force of the spring 64. When the mobile core is attracted toward the electromagnet, a plunger (a needle) is displaced in a valve opening direction for opening the control valve so that the valve member is limited from being seated.
When the intake stroke is finished and a pumping stroke is started, a pressure in the pump chamber is increased. The control valve is prohibited from being closed even when the pressure in the pump chamber is increased, because the valve member is prohibited from being seated as discussed before. Thus, a part of fuel returns to the fuel connection part from the pump chamber.
When an engine is running at a high speed, the solenoid valve needs to be highly responsive. Specifically, when the electromagnet is energized, the needle needs to be immediately displaced to the valve opening direction.
According to the solenoid valve described in FIGS. 3 and 4 of Japanese Unexamined Patent Publication No. 2002-521616, the mobile core is biased by the spring 64 to be spaced away from the valve member. Thus, when the electromagnet is not energized, the mobile core is disposed at the furthest position from the valve member. In other words, there is a large air gap between the mobile core and a stopper disc 78u. Because the mobile core is biased by the spring 64 to be spaced away from the valve member, and also because of the large air gap, a large current needs to be applied to the electromagnet by a current drive to immediately displace the needle. Thus, the solenoid valve described in FIGS. 3 and 4 of Japanese Unexamined Patent Publication No. 2002-521616 has a disadvantage that a cost of the drive circuit for driving the electromagnet is increased if a substantial response speed needs to be achieved.